Limitations of adjustment load range of 325 MW combined cycle plant

This article presents an analysis of limitations of the adjustment load range of a 325 MW combined cycle power unit (CCP-325) based on two GTE-110 gas turbines. It is noted that CCP-325 should have the minimum capacity of about 30% of the nominal capacity (with one GTE-110 disabled) to ensure reliable operation without time restrictions. The article describes the features of GTE-110 operation:
1) Operation with inlet guide vanes (IGV) of the compressor fully opened at the GTE-110 capacity below 65% of nominal capacity required by the manufacturer.
2) GTE-110 capacity changes abruptly in the 18-48 MW range.
The following factors were taken into account to determine the CCP-325 minimum allowable capacity:
1) The minimum allowable temperature of high-pressure inlet steam set by the manufacturer is 473°C (emergency shutdown at 440°C).
2) GTE-110 is operated with gas fed into the both areas of the combustion chamber.
3) GTE-110 operation at 65-100% of the GTE-110 capacity within the range of compressor IGV adjustment.
The article shows that the minimum allowable GTE-110 capacity is determined by the lowest allowable temperature of high-pressure inlet steam, that is 450°C, on condition that the gas feeding algorithm is adjusted. Based on this conclusion, calculations of the CCP-325 minimum capacity are performed. Results are presented as follows:
1) The CCP-325 adjustment load range is 69–100% with account to the GTE-110 manufacturer’s restriction.
2) Implementation of the recommendations provided in the article will allow reduction of the CCP-325 minimum capacity to 42% of the nominal capacity.
3) Partial disabling of CCP-325 equipment will allow reduction of CCP-325 minimum capacity to 34% of the nominal capacity for operating GTE-110 and to 20% if the suggested recommendations are implemented.
It is demonstrated that energy effi ciency of unloading CCP-325 is achieved with a capacity of at least 78 MW with incomplete set of equipment and 139 MW with complete set of equipment.

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